LOCKSTAT(1M) Maintenance Commands LOCKSTAT(1M)


NAME


lockstat - report kernel lock and profiling statistics

SYNOPSIS


lockstat [-ACEHI] [-e event_list] [-i rate]
[-b | -t | -h | -s depth] [-n nrecords]
[-l lock [, size]] [-d duration]
[-f function [, size]] [-T] [-ckgwWRpP] [-D count]
[-o filename] [-x opt [=val]] command [args]


DESCRIPTION


The lockstat utility gathers and displays kernel locking and profiling
statistics. lockstat allows you to specify which events to watch (for
example, spin on adaptive mutex, block on read access to rwlock due to
waiting writers, and so forth) how much data to gather for each event,
and how to display the data. By default, lockstat monitors all lock
contention events, gathers frequency and timing data about those events,
and displays the data in decreasing frequency order, so that the most
common events appear first.


lockstat gathers data until the specified command completes. For example,
to gather statistics for a fixed-time interval, use sleep(1) as the
command, as follows:


example# lockstat sleep 5


When the -I option is specified, lockstat establishes a per-processor
high-level periodic interrupt source to gather profiling data. The
interrupt handler simply generates a lockstat event whose caller is the
interrupted PC (program counter). The profiling event is just like any
other lockstat event, so all of the normal lockstat options are
applicable.


lockstat relies on DTrace to modify the running kernel's text to
intercept events of interest. This imposes a small but measurable
overhead on all system activity, so access to lockstat is restricted to
super-user by default. The system administrator can permit other users to
use lockstat by granting them additional DTrace privileges. Refer to the
Dynamic Tracing Guide for more information about DTrace security
features.

OPTIONS


The following options are supported:

Event Selection


If no event selection options are specified, the default is -C.

-A

Watch all lock events. -A is equivalent to -CH.


-C

Watch contention events.


-E

Watch error events.


-e event_list

Only watch the specified events. event list is a comma-separated list
of events or ranges of events such as 1,4-7,35. Run lockstat with no
arguments to get a brief description of all events.


-H

Watch hold events.


-I

Watch profiling interrupt events.


-i rate

Interrupt rate (per second) for -I. The default is 97 Hz, so that
profiling doesn't run in lockstep with the clock interrupt (which
runs at 100 Hz).


Data Gathering


-x arg[=val]

Enable or modify a DTrace runtime option or D compiler option. The
list of options is found in the . Boolean options are enabled by
specifying their name. Options with values are set by separating the
option name and value with an equals sign (=).


Data Gathering (Mutually Exclusive)
-b

Basic statistics: lock, caller, number of events.


-h

Histogram: Timing plus time-distribution histograms.


-s depth

Stack trace: Histogram plus stack traces up to depth frames deep.


-t

Timing: Basic plus timing for all events [default].


Data Filtering


-d duration

Only watch events longer than duration.


-f func[,size]

Only watch events generated by func, which can be specified as a
symbolic name or hex address. size defaults to the ELF symbol size if
available, or 1 if not.


-l lock[,size]

Only watch lock, which can be specified as a symbolic name or hex
address. size defaults to the ELF symbol size or 1 if the symbol size
is not available.


-n nrecords

Maximum number of data records.


-T

Trace (rather than sample) events [off by default].


Data Reporting


-c

Coalesce lock data for lock arrays (for example, pse_mutex[]).


-D count

Only display the top count events of each type.


-g

Show total events generated by function. For example, if foo() calls
bar() in a loop, the work done by bar() counts as work generated by
foo() (along with any work done by foo() itself). The -g option works
by counting the total number of stack frames in which each function
appears. This implies two things: (1) the data reported by -g can be
misleading if the stack traces are not deep enough, and (2) functions
that are called recursively might show greater than 100% activity. In
light of issue (1), the default data gathering mode when using -g is
-s 50.


-k

Coalesce PCs within functions.


-o filename

Direct output to filename.


-P

Sort data by (count * time) product.


-p

Parsable output format.


-R

Display rates (events per second) rather than counts.


-W

Whichever: distinguish events only by caller, not by lock.


-w

Wherever: distinguish events only by lock, not by caller.


DISPLAY FORMATS


The following headers appear over various columns of data.

Count or ops/s

Number of times this event occurred, or the rate (times per second)
if -R was specified.


indv

Percentage of all events represented by this individual event.


genr

Percentage of all events generated by this function.


cuml

Cumulative percentage; a running total of the individuals.


rcnt

Average reference count. This will always be 1 for exclusive locks
(mutexes, spin locks, rwlocks held as writer) but can be greater than
1 for shared locks (rwlocks held as reader).


nsec

Average duration of the events in nanoseconds, as appropriate for the
event. For the profiling event, duration means interrupt latency.


Lock

Address of the lock; displayed symbolically if possible.


CPU+PIL

CPU plus processor interrupt level (PIL). For example, if CPU 4 is
interrupted while at PIL 6, this will be reported as cpu[4]+6.


Caller

Address of the caller; displayed symbolically if possible.


EXAMPLES


Example 1: Measuring Kernel Lock Contention



example# lockstat sleep 5
Adaptive mutex spin: 2210 events in 5.055 seconds (437 events/sec)


Count indv cuml rcnt nsec Lock Caller
------------------------------------------------------------------------
269 12% 12% 1.00 2160 service_queue background+0xdc
249 11% 23% 1.00 86 service_queue qenable_locked+0x64
228 10% 34% 1.00 131 service_queue background+0x15c
68 3% 37% 1.00 79 0x30000024070 untimeout+0x1c
59 3% 40% 1.00 384 0x300066fa8e0 background+0xb0
43 2% 41% 1.00 30 rqcred_lock svc_getreq+0x3c
42 2% 43% 1.00 341 0x30006834eb8 background+0xb0
41 2% 45% 1.00 135 0x30000021058 untimeout+0x1c
40 2% 47% 1.00 39 rqcred_lock svc_getreq+0x260
37 2% 49% 1.00 2372 0x300068e83d0 hmestart+0x1c4
36 2% 50% 1.00 77 0x30000021058 timeout_common+0x4
36 2% 52% 1.00 354 0x300066fa120 background+0xb0
32 1% 53% 1.00 97 0x30000024070 timeout_common+0x4
31 1% 55% 1.00 2923 0x300069883d0 hmestart+0x1c4
29 1% 56% 1.00 366 0x300066fb290 background+0xb0
28 1% 57% 1.00 117 0x3000001e040 untimeout+0x1c
25 1% 59% 1.00 93 0x3000001e040 timeout_common+0x4
22 1% 60% 1.00 25 0x30005161110 sync_stream_buf+0xdc
21 1% 60% 1.00 291 0x30006834eb8 putq+0xa4
19 1% 61% 1.00 43 0x3000515dcb0 mdf_alloc+0xc
18 1% 62% 1.00 456 0x30006834eb8 qenable+0x8
18 1% 63% 1.00 61 service_queue queuerun+0x168
17 1% 64% 1.00 268 0x30005418ee8 vmem_free+0x3c
[...]

R/W reader blocked by writer: 76 events in 5.055 seconds (15 events/sec)

Count indv cuml rcnt nsec Lock Caller
------------------------------------------------------------------------
23 30% 30% 1.00 22590137 0x300098ba358 ufs_dirlook+0xd0
17 22% 53% 1.00 5820995 0x3000ad815e8 find_bp+0x10
13 17% 70% 1.00 2639918 0x300098ba360 ufs_iget+0x198
4 5% 75% 1.00 3193015 0x300098ba360 ufs_getattr+0x54
3 4% 79% 1.00 7953418 0x3000ad817c0 find_bp+0x10
3 4% 83% 1.00 935211 0x3000ad815e8 find_read_lof+0x14
2 3% 86% 1.00 16357310 0x300073a4720 find_bp+0x10
2 3% 88% 1.00 2072433 0x300073a4720 find_read_lof+0x14
2 3% 91% 1.00 1606153 0x300073a4370 find_bp+0x10
1 1% 92% 1.00 2656909 0x300107e7400 ufs_iget+0x198
[...]


Example 2: Measuring Hold Times



example# lockstat -H -D 10 sleep 1
Adaptive mutex spin: 513 events


Count indv cuml rcnt nsec Lock Caller
-------------------------------------------------------------------------
480 5% 5% 1.00 1136 0x300007718e8 putnext+0x40
286 3% 9% 1.00 666 0x3000077b430 getf+0xd8
271 3% 12% 1.00 537 0x3000077b430 msgio32+0x2fc
270 3% 15% 1.00 3670 0x300007718e8 strgetmsg+0x3d4
270 3% 18% 1.00 1016 0x300007c38b0 getq_noenab+0x200
264 3% 20% 1.00 1649 0x300007718e8 strgetmsg+0xa70
216 2% 23% 1.00 6251 tcp_mi_lock tcp_snmp_get+0xfc
206 2% 25% 1.00 602 thread_free_lock clock+0x250
138 2% 27% 1.00 485 0x300007c3998 putnext+0xb8
138 2% 28% 1.00 3706 0x300007718e8 strrput+0x5b8
-------------------------------------------------------------------------
[...]


Example 3: Measuring Hold Times for Stack Traces Containing a Specific


Function

example# lockstat -H -f tcp_rput_data -s 50 -D 10 sleep 1
Adaptive mutex spin: 11 events in 1.023 seconds (11
events/sec)


-------------------------------------------------------------------------
Count indv cuml rcnt nsec Lock Caller
9 82% 82% 1.00 2540 0x30000031380 tcp_rput_data+0x2b90

nsec ------ Time Distribution ------ count Stack
256 |@@@@@@@@@@@@@@@@ 5 tcp_rput_data+0x2b90
512 |@@@@@@ 2 putnext+0x78
1024 |@@@ 1 ip_rput+0xec4
2048 | 0 _c_putnext+0x148
4096 | 0 hmeread+0x31c
8192 | 0 hmeintr+0x36c
16384 |@@@ 1
sbus_intr_wrapper+0x30
[...]

Count indv cuml rcnt nsec Lock Caller
1 9% 91% 1.00 1036 0x30000055380 freemsg+0x44

nsec ------ Time Distribution ------ count Stack
1024 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1 freemsg+0x44
tcp_rput_data+0x2fd0
putnext+0x78
ip_rput+0xec4
_c_putnext+0x148
hmeread+0x31c
hmeintr+0x36c

sbus_intr_wrapper+0x30
-------------------------------------------------------------------------
[...]


Example 4: Basic Kernel Profiling




For basic profiling, we don't care whether the profiling interrupt
sampled foo()+0x4c or foo()+0x78; we care only that it sampled somewhere
in foo(), so we use -k. The CPU and PIL aren't relevant to basic
profiling because we are measuring the system as a whole, not a
particular CPU or interrupt level, so we use -W.


example# lockstat -kIW -D 20 ./polltest
Profiling interrupt: 82 events in 0.424 seconds (194
events/sec)


Count indv cuml rcnt nsec Hottest CPU+PIL Caller
-----------------------------------------------------------------------
8 10% 10% 1.00 698 cpu[1] utl0
6 7% 17% 1.00 299 cpu[0] read
5 6% 23% 1.00 124 cpu[1] getf
4 5% 28% 1.00 327 cpu[0] fifo_read
4 5% 33% 1.00 112 cpu[1] poll
4 5% 38% 1.00 212 cpu[1] uiomove
4 5% 43% 1.00 361 cpu[1] mutex_tryenter
3 4% 46% 1.00 682 cpu[0] write
3 4% 50% 1.00 89 cpu[0] pcache_poll
3 4% 54% 1.00 118 cpu[1] set_active_fd
3 4% 57% 1.00 105 cpu[0] syscall_trap32
3 4% 61% 1.00 640 cpu[1] (usermode)
2 2% 63% 1.00 127 cpu[1] fifo_poll
2 2% 66% 1.00 300 cpu[1] fifo_write
2 2% 68% 1.00 669 cpu[0] releasef
2 2% 71% 1.00 112 cpu[1] bt_getlowbit
2 2% 73% 1.00 247 cpu[1] splx
2 2% 76% 1.00 503 cpu[0] mutex_enter
2 2% 78% 1.00 467 cpu[0]+10 disp_lock_enter
2 2% 80% 1.00 139 cpu[1] default_copyin
-----------------------------------------------------------------------
[...]


Example 5: Generated-load Profiling




In the example above, 5% of the samples were in poll(). This tells us how
much time was spent inside poll() itself, but tells us nothing about how
much work was generated by poll(); that is, how much time we spent in
functions called by poll(). To determine that, we use the -g option. The
example below shows that although polltest spends only 5% of its time in
poll() itself, poll()-induced work accounts for 34% of the load.


Note that the functions that generate the profiling interrupt
(lockstat_intr(), cyclic_fire(), and so forth) appear in every stack
trace, and therefore are considered to have generated 100% of the load.
This illustrates an important point: the generated load percentages do
not add up to 100% because they are not independent. If 72% of all stack
traces contain both foo() and bar(), then both foo() and bar() are 72%
load generators.


example# lockstat -kgIW -D 20 ./polltest
Profiling interrupt: 80 events in 0.412 seconds (194 events/sec)


Count genr cuml rcnt nsec Hottest CPU+PIL Caller
-------------------------------------------------------------------------
80 100% ---- 1.00 310 cpu[1] lockstat_intr
80 100% ---- 1.00 310 cpu[1] cyclic_fire
80 100% ---- 1.00 310 cpu[1] cbe_level14
80 100% ---- 1.00 310 cpu[1] current_thread
27 34% ---- 1.00 176 cpu[1] poll
20 25% ---- 1.00 221 cpu[0] write
19 24% ---- 1.00 249 cpu[1] read
17 21% ---- 1.00 232 cpu[0] write32
17 21% ---- 1.00 207 cpu[1] pcache_poll
14 18% ---- 1.00 319 cpu[0] fifo_write
13 16% ---- 1.00 214 cpu[1] read32
10 12% ---- 1.00 208 cpu[1] fifo_read
10 12% ---- 1.00 787 cpu[1] utl0
9 11% ---- 1.00 178 cpu[0] pcacheset_resolve
9 11% ---- 1.00 262 cpu[0] uiomove
7 9% ---- 1.00 506 cpu[1] (usermode)
5 6% ---- 1.00 195 cpu[1] fifo_poll
5 6% ---- 1.00 136 cpu[1] syscall_trap32
4 5% ---- 1.00 139 cpu[0] releasef
3 4% ---- 1.00 277 cpu[1] polllock
-------------------------------------------------------------------------
[...]


Example 6: Gathering Lock Contention and Profiling Data for a Specific


Module


In this example we use the -f option not to specify a single function,
but rather to specify the entire text space of the sbus module. We gather
both lock contention and profiling statistics so that contention can be
correlated with overall load on the module.


example# modinfo | grep sbus
24 102a8b6f b8b4 59 1 sbus (SBus (sysio) nexus driver)


example# lockstat -kICE -f 0x102a8b6f,0xb8b4 sleep 10
Adaptive mutex spin: 39 events in 10.042 seconds (4 events/sec)


Count indv cuml rcnt nsec Lock Caller
-------------------------------------------------------------------------
15 38% 38% 1.00 206 0x30005160528 sync_stream_buf
7 18% 56% 1.00 14 0x30005160d18 sync_stream_buf
6 15% 72% 1.00 27 0x300060c3118 sync_stream_buf
5 13% 85% 1.00 24 0x300060c3510 sync_stream_buf
2 5% 90% 1.00 29 0x300060c2d20 sync_stream_buf
2 5% 95% 1.00 24 0x30005161cf8 sync_stream_buf
1 3% 97% 1.00 21 0x30005161110 sync_stream_buf
1 3% 100% 1.00 23 0x30005160130 sync_stream_buf
[...]

Adaptive mutex block: 9 events in 10.042 seconds (1 events/sec)

Count indv cuml rcnt nsec Lock Caller
-------------------------------------------------------------------------
4 44% 44% 1.00 156539 0x30005160528 sync_stream_buf
2 22% 67% 1.00 763516 0x30005160d18 sync_stream_buf
1 11% 78% 1.00 462130 0x300060c3510 sync_stream_buf
1 11% 89% 1.00 288749 0x30005161110 sync_stream_buf
1 11% 100% 1.00 1015374 0x30005160130 sync_stream_buf
[...]

Profiling interrupt: 229 events in 10.042 seconds (23 events/sec)

Count indv cuml rcnt nsec Hottest CPU+PIL Caller

-------------------------------------------------------------------------
89 39% 39% 1.00 426 cpu[0]+6 sync_stream_buf
64 28% 67% 1.00 398 cpu[0]+6 sbus_intr_wrapper
23 10% 77% 1.00 324 cpu[0]+6 iommu_dvma_kaddr_load
21 9% 86% 1.00 512 cpu[0]+6 iommu_tlb_flush
14 6% 92% 1.00 342 cpu[0]+6 iommu_dvma_unload
13 6% 98% 1.00 306 cpu[1] iommu_dvma_sync
5 2% 100% 1.00 389 cpu[1] iommu_dma_bindhdl
-------------------------------------------------------------------------
[...]


Example 7: Determining the Average PIL (processor interrupt level) for a


CPU

example# lockstat -Iw -l cpu[3] ./testprog

Profiling interrupt: 14791 events in 152.463 seconds (97 events/sec)

Count indv cuml rcnt nsec CPU+PIL Hottest Caller

-----------------------------------------------------------------------
13641 92% 92% 1.00 253 cpu[3] (usermode)
579 4% 96% 1.00 325 cpu[3]+6 ip_ocsum+0xe8
375 3% 99% 1.00 411 cpu[3]+10 splx
154 1% 100% 1.00 527 cpu[3]+4 fas_intr_svc+0x80
41 0% 100% 1.00 293 cpu[3]+13 send_mondo+0x18
1 0% 100% 1.00 266 cpu[3]+12 zsa_rxint+0x400
-----------------------------------------------------------------------
[...]


Example 8: Determining which Subsystem is Causing the System to be Busy



example# lockstat -s 10 -I sleep 20

Profiling interrupt: 4863 events in 47.375 seconds (103 events/sec)

Count indv cuml rcnt nsec CPU+PIL Caller

-----------------------------------------------------------------------
1929 40% 40% 0.00 3215 cpu[0] usec_delay+0x78
nsec ------ Time Distribution ------ count Stack
4096 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1872 ata_wait+0x90
8192 | 27 acersb_get_intr_status+0x34
16384 | 29 ata_set_feature+0x124
32768 | 1 ata_disk_start+0x15c
ata_hba_start+0xbc
ghd_waitq_process_and \
_mutex_hold+0x70
ghd_waitq_process_and \
_mutex_exit+0x4
ghd_transport+0x12c
ata_disk_tran_start+0x108
-----------------------------------------------------------------------
[...]


SEE ALSO


dtrace(1M), plockstat(1M), attributes(5), lockstat(7D), mutex(9F),
rwlock(9F)


Dynamic Tracing Guide:


https://illumos.org/books/dtrace/


NOTES


Tail-call elimination can affect call sites. For example, if foo()+0x50
calls bar() and the last thing bar() does is call mutex_exit(), the
compiler can arrange for bar() to branch to mutex_exit() with a return
address of foo()+0x58. Thus, the mutex_exit() in bar() will appear as
though it occurred at foo()+0x58.


The PC in the stack frame in which an interrupt occurs can be bogus
because, between function calls, the compiler is free to use the return
address register for local storage.


When using the -I and -s options together, the interrupted PC will
usually not appear anywhere in the stack since the interrupt handler is
entered asynchronously, not by a function call from that PC.


The lockstat technology is provided on an as-is basis. The format and
content of lockstat output reflect the current kernel implementation and
are therefore subject to change in future releases.


December 10, 2017 LOCKSTAT(1M)